1. Field of the Invention
The present invention relates to a gas barrier substrate having a high gas barrier property and a flatness, to be used for a display substrate such as an organic electroluminescent (hereinafter it may abbreviated as organic EL) device or the like.
2. Description of the Related Art
Conventionally, for example, as a supporting substrate for a display substrate such as an organic EL display, those using a glass substrate are known. However, the glass substrates have shortcomings of heaviness, hardness and easily crackable. Then, recently, in order to solve the problems of the glass substrates, a plastic substrate has been proposed.
However, although the plastic substrates are light-weight, flexible and hardly crackable, they have a poorer gas barrier property compared with the glass substrates so that it has been difficult to maintain the performance of the display device for a long time.
Moreover, for example, when a supporting substance is used for a display device such as an organic EL device, the gas barrier property to oxygen or water vapor is required, because the light emission deterioration occur when a light emitting layer of the organic EL device contact with a water vapor or oxygen. Moreover, since the process under a high temperature is necessary to form an organic EL device, the heat resistance is also required for the supporting substrate. Moreover, when the supporting substrate does not have enough flatness, a defect can be generated in the gas barrier property due to a pin hole, a projection or the like, or since the organic EL layer such as the light emitting layer is a thin film, the organic EL layer cannot be formed evenly due to a pin hole, a projection or the like so that a dark spot is considered to be generated in the organic EL display. Moreover, when the display is installed and used for a long time, the supporting substrate is required to be stable to the electric potential and the temperature rise. This is because a problem of the modulation of the light emission or the light of the display can be generated when the supporting substrate is unstable to the electric potential or the temperature rise. In view of these points, a method of providing the properties to the plastic substrate has been required.
Therefore, conventionally, for providing the gas barrier property to a plastic substrate, the following proposal has been provided. For example, according to Japanese Patent Application Laid-Open (JP-A) No. 7-164591, a high gas barrier property is achieved by providing an inorganic deposition film as the first layer on a substrate made of a polymer resin composition, and laminating, as the second layer, a gas barrier property film produced by applying a coating agent containing, as the main agent, an aqueous solution including one or more kinds of an alkoxide and/or a hydrolyzed product thereof, and a tin chloride, or a water/alcohol mixture solution, heating and drying.
Moreover, according to JP-A No. 7-268115, a high gas barrier property is achieved by providing an inorganic deposition film as the first layer on a substrate made of a polymer resin composition, and laminating, as the second layer, a gas barrier property film produced by applying a coating agent containing, as the main agent, a mixture solution of one or more kinds of an alkoxide or a hydrolyzed product thereof, and an isocyanate compound having at least two isocyanate groups in the molecule, heating and drying.
Moreover, according to JP-A No. 11-222508, a gas barrier property is achieved by providing an inorganic deposition film made of a SiO2 on a substrate having the excellent heat resistance, mechanical strength, and in particular, shock resistance by including a component containing an alicyclic hydrocarbon skeleton bis(meth)acrylate, a mercapto compound, and a monofunctional (meth)acrylate).
However, according to JP-A Nos. 7-164591, 7-268115, the application is limited to the packaging field such as the food and the medical products. Furthermore, as to the gas barrier property, the water vapor transmission rate (hereinafter it is referred to also as the WVTR) is about 0.1 g/m2/day, and the oxygen transmission rate (hereinafter it is referred to also as the OTR) is about 0.3 cc/m2/day·atm, and thus it is insufficient. Moreover, according to JP-A No. 11-222508, its application is in the display field, in particular, the liquid crystal display panel. Although the gas barrier property is achieved by providing an inorganic deposition film made of a SiO2 on a substrate, the oxygen transmission rate remains at 1 cc/m2/day·atm so that it is not sufficient as the water proof property for preventing deterioration of, for example, the light emitting layer of the organic EL device.
Moreover, as to the surface flatness, it is not discussed in any of the patent documents.
Furthermore, recently, when using a glass substrate as a thin film, improvement of the gas transmission rate is required in accordance with the high precision of the organic EL display.